Numbers 6:21

6:21 “This is the law of the Nazirite who vows to the Lord his offering according to his separation, as well as whatever else he can provide. Thus he must fulfill his vow that he makes, according to the law of his separation.”

Numbers 30:2

30:2 If a man makes a vow to the Lord or takes an oath of binding obligation on himself, he must not break his word, but must do whatever he has promised.